As a promising candidate, the fluorooxoborate has enkindled new explorations of nonlinear optical materials to meet the deep-ultraviolet criteria. However, big challenges and open questions still remain facing this exciting new field, especially the birefringence and dispersion of refractive index which are fundamental parameters for determining the phasematching second harmonic generation wavelength. Here we designed possible anionic groups in fluorooxoborates, and analyzed the optical anisotropy to check its influence on birefringence, which was proved further by the response electronic distribution anisotropy approximation. The functional modules modulating birefringence in fluorooxoborates were explored systematically. We developed an approach for evaluating the behavior of the refractive index dispersions and found that the fluorooxoborates had small refractive index dispersions owing to the introduction of fluorooxoborate modules. Our results demonstrate that fluorooxoborates can be utilized to realize short phase-matching wavelength markedly and offer a path toward novel performance-driven materials design.